[RFC] Add extra ehlo() and starttls() for gmail smtp

[Harald Meland]

[Aaron Bentley]

> Harald Meland wrote:
>> [Keir Mierle]
>> An SMTP client shouldn't try to do STARTTLS until after EHLO has
>> succeeded (and indicated that STARTTLS indeed is among the extensions
>> that the server supports).  The client should also fall back to HELO
>> if EHLO fails, and verify whether HELO fails.
>
> This looks like a nice improvement.  There's just one thing I wonder about:
>
>> +                (code, message) = self._connection.starttls()
>> +                if (200 <= code <= 299):
>
> This seems to mean that if starttls fails, we'll use unencrypted
> SMTP.

Well, we will at least *try* to use unencrypted SMTP. :-)

> I'm not sure whether we should fail in this situation, give a
> warning, or silently continue.

Hmmm.  Maybe a separate config setting, e.g.

  smtp_tls = required | preferred | off

?

A somewhat related question is whether we ought to support SSL
(typically found on port 465), and not just STARTTLS-initiated TLS
(typically found on port 25 and/or 587).

> It seems like if people expect their privacy to be protected and
> it's not, that's a violation of trust.  But OTOH, I don't know
> whether people would expect privacy here.

I used "smtp_server = smtp.gmail.com:587" when testing this change,
and as I know that that SMTP server won't allow SMTP AUTH until after
STARTTLS has succeeded, I wouldn't want Bazaar to spew my credentials
over an unencrypted connection just to see the server reject the
authentication attempt.

However, for servers that allow SMTP AUTH pre-STARTTLS, the issue
isn't as clear-cut.
-- 
Harald